9
Time dependence of the position of a nucleus and the two corresponding edges of the cell Time dependence of the velocity of the above nucleus

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Distribution of the maximum velocities in an ensemble of C6 cells Peaks are at +/- 50 micron/hour Distribution of the duration of the periods in an ensemble of the above cells. Peak is at 5 hours

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Effect of drugs Inhibition of microtubule dynamics: e.g., adding after one day 20 nM Vinblastine blocks auto-reverse migration Drugs targeting actin and molecular motors did not have effect

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Results from immunocytochemistry The microtubules run parallel to the main axis (even over the nucleus, where their number density is significantly smaller) Staining for microtubules

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Centrosome position is correlated with the direction of nuclear motion Staining for  tubulin reveals that the centrosome is never located in the front part of the nucleus no migration centrosome

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Forces involved in nuclear migration From data on the viscosity of the cell plasma and the velocity/size of the nucleus, using Stoke’s law, we estimate the force needed to be in the range 10 - 100 pN The polimerization of one microtubule generates appr. 1pN, thus a few dozen can push/pull the nucleus Microtubule polymerization dynamics is a source of force (From Molecular Biology of the Cell )

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MODEL Based on our following observations: a) Array of microtubules is highly organized b) Centrosome is on the trailing side c) Estimated force is high enough ( dynein can play some role close to the cortex) Reversal of direction is due to the repositioning of the centrosome (pushed by microtubules) at the edge of the cell Only microtubules playing the most important role in the migration of the nucleus are shown (there are many more)

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CONCLUSIONS - First direct observation of oscillatory nuclear migration in vertebrate cells - Proposition/demonstration of a nuclear motility assay for in vitro study - Determination of the main characteristics of auto-reverse nuclear migration - Evidence for the major role of MT dynamics and the position of the centrosome - Presentation of a corresponding model Acknowledgements: Hung. Natl. Sci Funds: OTKA and NKFP